lesson 0: CELLULAR TRANSPORT
PASSIVE and active
All cells live at least partly in touch with a water solution. In order to live, all cells must take in nutrients and eliminate wastes. Somehow nutrients and waste materials must cross the cell membrane between the solution outside the cell and the solution inside the cell.
Several processes are involved in moving materials across the cell membrane. These processes can be classified as either passive or active transport. Passive Transport is the movement of a substance across a cell membrane without the usage of energy. Active Transport uses the energy of the cell to move a substance across the cell membrane. Following is a summary of the different transport systems in the cell: